1. Field of the Invention
A recent innovation in herbicide application equipment for weed control amongst field crops is the roller applicator. This device selectively dispenses herbicide solution onto weeds protruding above crop plants by direct contact with an absorbent roller. The roller is normally wetted by means of a perforated manifold pipe which drips herbicide at preestablished intervals along its length. With this applicator, a nonselective, translocated herbicide can be used in controlling tall growing weed escapes at an application rate of only 20% of that required by a broadcast sprayer. However, existing roller applicators have suffered the problem of maintaining the proper herbicide concentration on the roller to effect weed control without excessive drippage onto the crops. This invention relates to an automatic moisture controller for use with these roller applicators.
2. Description of the Prior Art
The concept of automatic moisture control is not in itself new, and has been applied to a variety of situations. For example, in U.S. Pat. No. 4,137,931 Hasenbeck discloses an irrigation control system in which soil matric potential as a function of water content is determined by a sensor, which in turn signals a solenoid water valve in a sprinkler line. A similar device is taught in an earlier patent by Hasenbeck. In U.S. Pat. No. 3,553,481 an irrigation system is automatically controlled by response to changes in resistance variation of subsurface sensors caused by changes in heat transfer as a function of soil moisture variation. While these control systems may be suitable for the irrigation of soil, neither is sufficiently condition-responsive to maintain the moisture concentration within a predetermined narrow range as would be required by the roller applicator.
Fegan, U.S. Pat. No. 3,376,877, shows an automatic moisture control system for particulate feed material on a conveyor. While this apparatus is designed to be more condition-responsive than the irrigation controllers discussed above, it is not suitable for control of the moisture on a nonuniformly wetted, unitary mass, such as a herbicide applicator.